1. Field of the Invention
The invention relates to a method and a device for suppressing vibrations in a printing press, in which a freely vibrating mass is used on a vibrating element.
In the drive of printing presses, such as sheet-fed presses, use is made inter alia of belt and gear mechanisms. In the gear train of a cyclically printing sheet-fed press, undesired excitation of vibrations occurs at various points, the vibrations not being of integer orders, that is to say, they do not repeat once, twice, or n times per printed sheet. Such excitation leads to vibrations of the same order that, in printing terms, manifest themselves as faults whose position changes from sheet to sheet. Such printing faults, which show themselves, for example, as stripes in the printed image, are more striking than faults whose position does not change from sheet to sheet. Typical causes of such faults in sheet-fed presses are belt drives and drives for distributor rolls, which do not exhibit any integer revolution orders.
Printing presses are generally driven by electric motors. The drive torque from an electric motor is fed through a belt drive into a gear train, from which the cylinders, drums, and rolls in the printing units are driven. Existing in the prior art is the determination of disruptive vibrations, for example, on a cylinder, by using a sensor and driving one or more electric motors such that the vibrations are reduced. In addition, active absorbers can be provided, which are likewise driven in a vibration-compensating manner. The drawback is the high outlay for determining the disruptive vibrations. In order to register the vibrations at all points at which they are produced, a large number of active absorbers would have to be used in addition to a large number of sensors.
Printing presses can be configured such that odd-numbered excited vibrations are avoided to the greatest possible extent. If a belt drive is used in the gear train, it is, in principle, not possible, because of the slip that is naturally present, to implement this over the entire speed range. In the case of sheet-fed presses, there are generally revolving elements in the area of the inking units that, as compared with the sheet-carrying cylinders, revolve with non-integer orders. Construction measures to keep the vibration excitation small by predefining appropriate tolerances are subject to fabrication limits. For example, the faults originating from a belt or the round running properties of distributor rolls can be reduced or improved only with increased design effort.
A printing press, as a structure capable of vibrating, exhibits natural resonances. One way of reducing undesired vibrations is to move resonances with odd-numbered orders into a non-critical speed range. In the case of sheet-fed presses, for example, the belt length in belt drives can be dimensioned suitably. The variation in the belt length has its limits in the overall space that is available and in the effect on the machine dynamics resulting from a longer and therefore softer belt. A further way lies in the use of an absorber matched to the natural frequency of a machine, as described in German Published, Non-Prosecuted Patent Application DE 199 14 613 A1.
East German Patent No. DD 130 321 A1 describes a device for absorbing torsional vibrations in the drive of presses, in which a pendulum is rotatably connected to one or more axes of rotation of a drive. The pendulum is matched to a specific excitation order of the rotational frequency range of the drive. The mass of rotation and stiffness of the pendulum are not changed.
German Published, Non-Prosecuted Patent Application DE 40 33 278 A1, corresponding to U.S. Pat. No. 5,235,909 to Gerstenberger et al., shows a device for damping flexural vibrations of printing-unit cylinders in which, in the printing-unit cylinder, one or more broadband-tuned dampers are provided, whose natural frequencies correspond to those of the respective printing-unit cylinder and that are deflected by centrifugal force in antiphase with the printing-unit cylinder. The mass of rotation and stiffness of the dampers remains constant.
Such systems, used in horizontally mounted cylinders, operate optimally only in a rotational speed range in which the force of gravity that acts can be neglected as compared with the centrifugal forces.
It is accordingly an object of the invention to provide a method and device for suppressing vibrations in a printing press that overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type and that develop their action over the entire rotational speed range with little outlay.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a method of suppressing vibrations in a printing press, including the steps of providing a mass vibrating freely with one degree of freedom on at least one element of the press, determining a rotational speed of the press and supplying the determined rotational speed to a control device, determining an actuating variable dependent upon the rotational speed with the control device and supplying the actuating variable to at least one actuator with the control device, and changing at least one vibration parameter of the mass with the actuator dependent upon the determined rotational speed.
The nub of the invention is that, on at least one element excited to vibrate in a printing press, a freely vibrating mass is used, at least one vibration parameter of the mass being changed continuously as a function of rotational speed by an actuator. At least one vibration parameter of the mass is set such that the frequency of the critically exciting vibration of the element of the press corresponds to the natural frequency of the freely vibrating mass.
The invention is suitable both for absorbing torsional and flexural vibrations. The system including actuator and vibration absorbing mass is used as far as possible on the element excited to vibrate or on an element in its immediate vicinity.
In accordance with another mode of the invention, a stiffness of the mass is changed with the actuator.
In accordance with a further mode of the invention, inertia of the mass is changed with the actuator.
With the objects of the invention in view, there is also provided a method of suppressing vibrations in a printing press, including the steps of providing a mass vibrating freely with one degree of freedom on at least one element of the press, determining a rotational speed of the press and supplying the determined rotational speed to a control device, and determining an actuating variable in the control device utilizing the rotational speed and supplying the actuating variable to at least one actuator, at least one vibration parameter of the mass being changed by the actuator dependent upon the rotational speed.
With the objects of the invention in view, there is also provided a device for suppressing vibrations in a printing press having at least one element, including a freely vibrating mass vibrating freely with one degree of freedom to be coupled to the at least one element, the mass having at least one vibration parameter, a rotational speed measuring configuration for determining a rotational speed of the press, an actuator connected to the mass for changing the vibration parameter, and a control device connected to the rotational speed measuring configuration and to the actuator.
In accordance with an added feature of the invention, the element has an axle, the mass displaceable on the axle, and at least one leaf spring is disposed parallel to the axle and is coupled to the element and the mass.
In accordance with an additional feature of the invention, there is provide an axle, the mass being displaceable on the axle, and at least one leaf spring disposed parallel to the axle and coupled to the element and the mass.
In accordance with yet another feature of the invention, the element is a revolving element having a radial direction, and the mass is displaceable in the radial direction of the revolving element.
In accordance with yet a further feature of the invention, an inhomogeneous, elastic rotating body is coupled to the actuator, rotates about an axis, and is coupled to the element and the mass.
In accordance with yet an added feature of the invention, the actuator is at least one electromagnet.
In accordance with yet an additional feature of the invention, the actuator is at least one pneumatic element.
In accordance with again another feature of the invention, the element is a revolving element and the actuator revolves with the revolving element.
In accordance with again a further feature of the invention, the press has a frame and the actuator is to be fixed to the frame.
In accordance with again an added feature of the invention, the actuator is disposed at the mass.
In accordance with again an additional feature of the invention, the actuator is disposed on the mass.
With the objects of the invention in view, in a printing press having at least one element, there is also provided a device for suppressing vibrations, including a freely vibrating mass vibrating freely with one degree of freedom coupled to the element, the mass having at least one vibration parameter, a rotational speed measuring configuration for determining a rotational speed of the press, an actuator connected to the mass for changing the vibration parameter, and a control device connected to the rotational speed measuring configuration and to the actuator.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for suppressing vibrations in a printing press, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.